Yup. You have it even worse then my ork bikers. At least someone else here now understands the "weakness" of bikers without 3+ armor. There is ALOT of AP4/AP5 ignores cover in the game.
Heck against jsut space marines things like
Simple flamers in a drop pod can drop behind your dudes and kill all your heavy weapons easy.
Thunder fires will just do hideous things to you. They don't have to declare which ammo they are using until after you decide to jink(look it up), So you are forced not only to jink to get a save but you don't even get your jink save... and they can snipe your special weapons.
Stern guard will just remove entire squads
Your bikes also get murdered if they get assaulted as well.